The present invention relates to a method of loosening particles, such as sand and scale, from internal surfaces of objects, particularly of metal. The invention has special application for castings, which after having been cast must be cleaned from various particles adhering to the surfaces which have been laid bare. External surfaces do not pose any major problems during the cleaning, and this is also the case as regards internal surfaces which are easily accessible from the outside. However, there are certain internal surfaces which are difficult or impossible to reach with tools from the outside. Blowing through with compressed air has not proved to be effective. Nor, has the use of a gas explosion outside the object, the hot combustion gases then being conveyed through the object, been sufficiently successful.